1. Field of the Invention
The present invention relates to a form measuring sensor and a form measuring instrument. More specifically, it relates to a form measuring sensor and a form measuring instrument for measuring a form of a workpiece by touching a stylus on a surface of a thread.
2. Description of Related Art
There are various shapes of workpiece to be measured. Among the workpiece, a thread of a threaded workpiece (threaded hole=internal thread, threaded shaft=external thread) has parameters (characteristic value) for defining characteristic thereof. Such parameters include thread pitch a, effective thread portion length b, incomplete thread portion c, threaded hole depth d etc. as shown in threaded hole 100 of FIG. 7. A coordinates measuring machine is used for measuring respective parameters a to d of the threaded hole 100.
In order to measure the thread by the coordinates measuring machine, a touch signal probe or a scanning probe can be used.
When a touch signal probe is used, the contact portion of the touch signal probe is brought into contact with the surface of the thread and the coordinates value at the time is read. The thread form is measured by obtaining coordinates value at a desired plurality of points by repeating the above operation.
On the other hand, when the scanning probe is used, the scanning probe and the thread are relatively moved while a contact portion of the scanning probe keeps in contact with the thread surface with a constant measurement force. The thread form is measured by continuously collecting the coordinates value of the contact portion.
However, following disadvantages occur in measuring the thread form using the above-described coordinates measuring machine.
When the touch signal probe is used to measure the workpiece, the touch signal probe has to touch the thread surface at respective points. Accordingly, for measuring the respective parameters of, for instance, the threaded hole 100, the data have to be continuously collected by multi-point measurement, so that considerable time is required for measurement.
On the other hand, when the scanning probe is used to measure the workpiece, since contact and separation are not required between the probe and the thread surface for respective points unlike the measurement using the touch signal probe, the data can be continuously collected within a short period of time. However, the scanning probe having a mechanism for continuously detecting the coordinates value of the contact portion while keeping the contact portion in contact with the thread surface is expensive in itself.
An object of the present invention is to provide a form measuring sensor and a form measuring instrument capable of continuously collecting workpiece surface form data within a short time and capable of being inexpensively constructed.
A form measuring sensor according to an aspect of the present invention includes: a stylus having a contact portion to be in contact with a workpiece surface at a first end; and a body for holding the stylus through an adaptor, the adaptor including a stylus attachment for a second end of the stylus to be attached, a body attachment to be attached to the body and an elastically deformable connector for connecting the stylus attachment and the body attachment, where the connector elastically deforms to allow a displacement of the stylus and the stylus attachment relative to the body attachment in accordance with a configuration of the surface of the workpiece, and where a deformation sensor for detecting the elastic deformation of the connector is provided.
In the present invention, the form measuring sensor is relatively moved in surface direction of the workpiece while the contact portion of the stylus keeps in contact with the surface of the workpiece. Then, the contact portion of the stylus scans the inner circumference of the workpiece and displaces in a direction approximately orthogonal with the relative movement, so that the stylus attachment of the adaptor attached with the stylus displaces in the same direction. On the other hand, since the body attachment of the adaptor is attached to the body relatively moving in the surface direction of the workpiece, the displacement direction becomes solely the relative movement direction. In other words, since the stylus attachment of the adaptor displaces approximately orthogonal with the relative movement direction and the body attachment does not displace relative to the body, the connector connecting the stylus attachment and the body attachment elastically deforms. Accordingly, the displacement of the stylus attachment, i.e. the displacement of the contact portion of the stylus can be represented by the elastic deformation of the connector. Continuous inner circumference form data of the workpiece can be collected within a short time by continuously detecting the elastic deformation of the connector with the deformation sensor.
The surface form of the workpiece is measured by detecting the elastic deformation of the connector which allows the displacement of the stylus by elastic deformation thereof, i.e. brings the stylus into contact with the workpiece with a constant measuring force. In other words, since the contact portion is brought into contact with the workpiece surface with a constant force and the displacement of the contact portion is continuously detected by the connector, the mechanism can be arranged simpler and more inexpensive than a scanning probe.
In the above arrangement, the stylus may preferably be formed in approximate L-shape and include a first arm extending along the surface of the workpiece with an end attached to the stylus attachment, and a second arm extending substantially orthogonal with the other end of the first arm and having the contact portion at an end thereof.
According to the above arrangement, since the stylus includes the first arm attached to the stylus attachment and extending along the surface of the workpiece, and the second arm extending approximately orthogonal with the first arm and having the contact portion, the stylus can be easily inserted into the threaded hole, and the contact portion can be securely brought into contact with the thread bottom of the threaded hole.
In the form measuring sensor according to the above arrangement of the present invention, the body may preferably be relatively moved along the surface of the workpiece while the contact portion of the stylus keeps in contact with the surface of the workpiece, and the contact portion of the stylus may preferably be disposed on a center line of the connector approximately parallel to the relative movement direction.
When the contact portion of the stylus scans the surface of the workpiece, some friction force is ordinarily generated between the contact portion and the workpiece surface. The friction force fluctuates according to measurement force applied to the contact portion and surface roughness of the workpiece etc. Specifically, when FIG. 6(A) is taken as an example, the stylus 110 is moved in a direction indicated by outlined arrow in the figure while an end of an approximately L-shaped stylus 110, i.e. a contact portion 111 keeps in contact with the surface of a workpiece W. At this time, measurement force Fv and friction force Ff are applied on the contact portion 111. When the length of the first arm 112 is L1 and the length of the second arm 113 is L2, a moment M1 applied to the other end 114 of the stylus 110 can be represented as follows:
M1=Fv*L1+Ff*L2 
When the connector of the adaptor is located on the other end 114 of the stylus 110, the moment M1 is applied on the connector to cause elastic deformation of the connector. The elastic deformation of the connector varies in accordance with surface form of the workpiece W. Accordingly, the surface configuration of the workpiece W can be detected by detecting and continuously recording the variation of the elastic deformation. In other words, the variation of the elastic deformation of the connector is preferably caused only by the displacement of the connector 111. However, as shown in FIG. 6(A), when the connector is at the other end 114 (on the first arm 112) being offset from the contact portion 111 by the length L2, the moment generated by fluctuating friction force Ff causes change in the elastic deformation of the connector.
Accordingly, in the present invention, as shown in FIG. 6(B) for instance, the contact portion 111 of the stylus 110 is disposed on a center line C of the connector 115 approximately parallel with the relative movement direction (in an outlined arrow direction in the figure). Specifically, the connector is not disposed on the other end 114 of the stylus 110, but the connector 115 is disposed at a position offset from the other end 114 (the first arm 112) by the length L2. Incidentally, the connector 115 may be disposed by connecting the other end 114 and the connector 115 with a member 116 shown in double-dotted line in the figure (a stylus attachment 116, for instance). Accordingly, since the friction force Ff applied to the contact portion 111 when the stylus 110 is moved in the direction of the outlined arrow in the figure is approximately parallel with the center line C of the connector 115, the moment caused by the friction force Ff is not applied on the connector 115, so that moment M2 applied to the connector 115 can be represented as follows:
M2=Fv*L1 
Accordingly, the friction force Ff applied to the contact portion 111 is not shown in the elastic deformation in a direction approximately orthogonal with the relative movement of the connector 15. Therefore, the influence of the friction force Ff fluctuating on account of surface roughness etc. can be eliminated, so that the displacement of the stylus in a direction approximately orthogonal with the relative movement can be reflected on the elastic deformation of the connector 115.
In the form measuring sensor according to the present invention, the deformation sensor may preferably include a strain gauge attached to the connector.
According to the above arrangement, since the deformation sensor for detecting the elastic deformation of the connector includes the strain gauge attached to the connector, inexpensive construction is possible.
In the form measuring sensor according to the present invention, the stylus may preferably be formed of a piano wire.
According to the above arrangement, since the stylus is made of piano wire, inexpensive construction is possible. Further, any desired form of stylus corresponding to the form of the workpiece can be easily formed by bending the piano wire.
A form measuring instrument according to another aspect of the present invention has a form measuring sensor according to the aforesaid aspect of the present invention, the instrument including: a holder for the form measuring sensor to be detachably attached; a relative movement mechanism for relatively moving the holder and the workpiece surface along a surface of the workpiece; and a controller for controlling the relative movement mechanism.
According to the above arrangement, the same function and effect as in the form measuring sensor of the aforesaid aspect of the present invention can be obtained. Specifically, since the contact portion contacts the workpiece surface with a constant force by the connector and the displacement of the connector is continuously detected by the connector, the continuous workpiece surface form data can be collected within a short time and inexpensive construction is possible.
The form measuring sensor according to the present invention may preferably be a sensor for measuring a thread form. By applying the present invention, a profile of a workpiece with relatively large undulations can be measured.
The form measuring instrument according to the present invention may preferably have the workpiece form sensor for measuring the thread form. Accordingly, the form measuring sensor can be easily exchanged with a sensor having appropriate size corresponding to the magnitude of the undulations of the thread.
In the form measuring instrument, a machining tool for threading the workpiece to form the thread may preferably be detachably attached to the holder.
According to the present arrangement, after, for instance, the tap is attached to the holder to form the threaded hole on the workpiece, the tap is detached from the holder and the form measuring sensor can be attached to measure the form of the workpiece.
Since thread cutting for finishing the workpiece into a final shape and measurement required after the thread cutting are conducted with the same instrument, the workpiece (object to be machined) is not necessary to be moved. Accordingly, positioning and position-calculation of the workpiece is not necessary, so that measurement time can be reduced.
In the form measuring instrument according to the present invention, a machining tool for forming a hole before threading of the thread on the workpiece may preferably be detachably attached to the holder.
According to the above arrangement, measurement of the workpiece form and formation of the workpiece on the object to be machined can be conducted simultaneously with measuring the workpiece form. In other words, the process from machining the hole before threading of the workpiece, to threading and measurement of the workpiece form can be conducted sequentially, so that machining and measurement time can be reduced.
A form measuring instrument according to another aspect of the present invention has the above-described form measuring sensor, which includes: a holder for the form measuring sensor to be detachably attached; a surface-direction relative movement mechanism for relatively moving the holder along a surface of the workpiece; a crosswise relative movement mechanism for relatively moving the holder along the workpiece surface in a direction intersecting the workpiece; and a controller for controlling the surface-direction relative movement mechanism and the crosswise relative movement mechanism, the controller controlling the crosswise relative movement mechanism so that an output of the deformation sensor becomes always constant.
According to the above arrangement, when the output of the deformation sensor changes in accordance with change in the attitude of the stylus on account of irregularities in measuring the workpiece surface by a scanning measurement, the controller controls the crosswise relative movement mechanism to change the stylus crosswise position relative to the workpiece surface, so that the attitude of the stylus relative to the workpiece surface stays always constant. Accordingly, great range of crosswise measurement can be obtained while avoiding circular error of the stylus.
In the above form measuring instrument, the form measuring sensor may preferably be a sensor for measuring a thread form. Accordingly, the form measuring sensor can be easily exchanged with a sensor of appropriate size in accordance with undulations of the thread form.